This description of related art is provided for the purpose of generally presenting a context for the disclosure that follows. Unless indicated otherwise herein, concepts described in this section are not prior art to this disclosure and are not admitted to be prior art by inclusion herein.
Many computing and electronic devices include a transceiver to facilitate communication over a wireless network or with other devices. These transceivers often use automatic gain control (AGC) to control amplification of received radio frequency (RF) signals, the power of which can vary due to many factors, such as transmitter proximity, multipath propagation, signal fading, and the like. To determine an appropriate amount of gain to apply to the RF signals, AGC circuits sample signal strength or amplitude of the RF signals with a peak detector. Most peak detectors, however, generate an output that not only indicates the amplitude of the RF signal of interest, but also includes a fundamental frequency and other harmonics of the RF signal.
To reject the fundamental frequency and other harmonics, which are often larger than the indication of the amplitude for the RF signal of interest, peak detectors often include a capacitor to filter out the fundamental frequency and other harmonics. This filter capacitor, however, slows operation of the peak detector and can prevent the AGC circuit from quickly responding to changes in RF signal amplitude. Alternatively, some peak detectors are implemented as fully differential circuits to address the fundamental frequency issue, but these differential circuits require a tail current source that reduces the voltage overhead of the circuit, increases circuit complexity, and consumes additional power.